At the present time, the main method for preventing tube or pipe corrosion in China makes use of hot bitumen or tar, which method was also the main method used in the major industrialized countries until recently. The lifetime of pipes treated with bitumen generally does not exceed ten years and in regions suffering from heavy corrosion conditions, the lifetime of such pipes does not exceed 5-7 years. There are many drawbacks to using such kinds of anticorrosive coating materials, e.g., the deformation rate limit is small, dripping flow occurs at elevated temperatures which damage the anticorrosive layer, the base produced at cathode protection harms the adhesion of the base painting, and microorganisms can cause erosion or damage thereon. Therefore, the weak points of the piping anticorrosive layer run the risk of being damaged at all times. This not only results in payment of large amounts of maintenance fees, but also results in a sizeable economic loss due to repairing and servicing of the pipings and interruption of the fluid transportation.
In recent years, the epoxy powder spraying method has been widely used for tube anticorrosion in many countries. In West Germany, for example, polyethylene powder coating material is employed for 90% of the anticorrosive applications with respect to gas piping as well as water supply piping. Epoxy powder coating material is widely used in western Europe and the United States. Since 1985, the Chinese Academy of Piping Research has successfully experimented with the epoxy powder spraying method for pipes and has commercialized such a method. Such steel-plastic composite pipes have a longer lifetime than those with the bitumen coating layer due to the raising of the deformation rate limit so that neither serious deformation will take place, nor will dripping cause damage. However, because epoxy powder is an organic material as is bitumen, it is susceptible to the aging problem of the coating layer. Along with the lapse of time, the rise and fall of temperature, the influence of the air humidity, as well as the acid, base, salt and water in the soil, the aging of the coating layer will accelerate. The age limit of both polyethylene and epoxy coating materials will barely exceed 20 years.
EP-0154513 (publication number) relates to glass compositions which are suitable for bonding to alloys, in particular, "Vitallium" (trademark) alloys. Its use is limited to implant tubes for use in surgical operations.
According to JP 60-273448, powdered glass spheres can be carried by a gas having a certain velocity and sprayed onto the surface of a base material, whereby these powder spheres form a molten film and adhere onto the surface of the base metal. The operational temperatures of the process are in the range of 700.degree. C. to 800.degree. C. and the use of the process is limited to only insulating material and fabrics.
The above art relates to glass that is sprayed onto a base material to form a composite material, as opposed to an inorganic material coating for anticorrosive purposes.
Therefore, it is necessary to provide a kind of pipe material which can eliminate the aging drawbacks of the present organic anticorrosive coating layer, to improve the anticorrosive performance of the pipings, and significantly lengthen their operational lifetime.